Method and system for controlling radio frequency power

ABSTRACT

A method for controlling pulsed power that includes measuring a first pulse of power from a power amplifier to obtain data. The method also includes generating a first signal to adjust a second pulse of delivered power, the first signal correlated to the data to minimize a power difference between a power set point and a substantially stable portion of the second pulse. The method also includes generating a second signal to adjust the second pulse of delivered power, the second signal correlated to the data to minimize an amplitude difference between a peak of the second pulse and the substantially stable portion of the second pulse.

TECHNICAL FIELD

This invention relates generally to control systems for plasmaprocessing equipment. In particular, the invention relates to methodsand systems for controlling radio frequency (RF) power delivery systems.

BACKGROUND

RF power delivery systems provide power to dynamic loads typically atfrequencies between about 400 kHz and about 200 MHz. Frequencies used inscientific, industrial and medical applications are approximately 2 MHz,13.56 MHz, and 27 MHz. Depending on the application, RF power isdelivered in a pulse and/or a continuous-wave mode to a load.Controlling delivered RF power has become increasingly important insemiconductor manufacturing as the dimensions of semiconductor featureshave continued to decrease. The ability to more precisely control RFpower parameters enables a semiconductor manufacturer to achieve smallersemiconductor features. This is particularly difficult, however, whenthe RF power is delivered to dynamic loads.

Various approaches exist for controlling pulsed RF power that isdelivered to dynamic loads. One approach is to use a look-up table ofknown operating parameters to control the amplitude and shape ofdelivered RF power on a pulse-by-pulse basis. Another approach is to useoptimal, constant parameter estimates around a nominal operating point.A third approach is to use high-bandwidth and/or high-speed components(e.g., a power-sensing circuit, a digital signal processor, and/or apre-regulator) to regulate the amplitude and shape of delivered RF poweron a pulse-by-pulse basis.

Problems exist, however, with each of these known approaches. In thefirst and second approaches, performance can degrade when processingconditions change and/or drift from the values in the look-up table orthe nominal operating point. In the third approach, high-speedcomponents add significant cost to control systems. Moreover, thecontrol system is susceptible to performance degradation due to theelectrical noise associated with high gain and high bandwidth systems.

Various approaches exist for switching an RF power delivery system froma pulsed mode to a continuous-wave mode. One known approach is to use anopen-loop system, where the input voltage to an RF power amplifier isfixed and pulses are generated by switching the RF power amplifier onand off. However, open-loop systems lack the ability to modify thedelivered power based on changes in operating conditions at the load.Further, open-loop systems are unable to compensate for the high numberof plasma oscillations that occur when using low-frequency pulses forplasma processing applications. Another known approach to switchingbetween pulsed and continuous-wave power is to temporarily stopprocessing between power-delivery modes. However, temporarily stoppingprocessing results in irregular processing after system start-up.Moreover, temporarily stopping processing results in an unstable plasmabecause the power is not constant. Finally, temporarily stoppingprocessing increases processing and cycle time.

SUMMARY

The invention generally features a system and method for controllingpulsed RF power provided to dynamic loads. One advantage is theinvention allows for a closed-loop system to more precisely andaccurately control pulsed RF power (e.g., high-frequency and/orlow-frequency pulsed power) delivered to dynamic loads. Anotheradvantage is the invention allows for pulse-by-pulse control of thedelivered RF power. In low-frequency systems, the invention can allowfor pulse-by-pulse control of the pulse shape (e.g., the “flatness”and/or the amplitude of the pulse). In some embodiments, pulse-by-pulsecontrol is achieved using lower-cost components than those used in knownsystems and methods. For example, lower-bandwidth and/or lower-speedcomponents can be used. Yet another advantage is the invention allowsfor pulse-by-pulse control of power delivered to a dynamic load withoutdegradation in, for example, the precision of the power parameters whenprocess conditions change and/or drift from the values in a look-uptable or nominal operating point. Another advantage is the inventionallows for repeatable, high-precision power control.

The invention, in one aspect, features a method for controlling pulsedpower. The method includes measuring a first pulse of power from a poweramplifier to obtain data. The method also includes generating a firstsignal to adjust a second pulse of delivered power, the first signalcorrelated to the data to minimize a power difference between a powerset point and a substantially stable portion of the second pulse. Themethod also includes generating a second signal to adjust the secondpulse of delivered power, the second signal correlated to the data tominimize an amplitude difference between a peak of the second pulse andthe substantially stable portion of the second pulse.

In some embodiments, the method includes providing the second signal asan input to a voltage source, the voltage source providing a voltage toa voltage to power converter. In some embodiments, the method includescorrelating the second signal to a time delay measured between thevoltage source receiving a set point and the voltage to power converteroutputting power. In some embodiments, the method includes comprisingcalculating a shape error between a peak of the first pulse and asubstantially stable portion of the first pulse. In some embodiments,the method also includes correlating the second signal to the shapeerror.

In some embodiments, the method includes calculating a power offsetbetween the power set point and a substantially stable portion of thefirst pulse. The method can include correlating the first signal to thepower offset. In some embodiments, the method includes providing thefirst signal as an input to a voltage source, the voltage sourceproviding a voltage to a voltage to power converter. The method caninclude correlating the first signal to a duty cycle input of thevoltage source.

The invention, in another aspect, features a method of power delivery.The method includes delivering power from a power amplifier in acontinuous-wave mode to a load. The method also includes generating asignal in a feedback loop to control the delivered power, the signalcorrelated to a power control algorithm. The method also includesadjusting a single variable in the control algorithm to transition thedelivered power from the continuous-wave mode to a pulsed mode.

In some embodiments, the method includes activating a switch in thefeedback loop based on an input corresponding to the single variable,the switch in electrical communication with a power amplifier. In someembodiments, the method includes filtering the data to provide asubstantially stable power measurement. In some embodiments, the methodincludes providing the signal as an input to a voltage source, thevoltage source providing a voltage to a voltage to power converter. Themethod can include correlating the signal to a duty cycle input of thevoltage source.

In some embodiments, the method includes calculating a power offsetbetween a power set point and the delivered power. In some embodiments,the method includes measuring the delivered power to obtain data. Insome embodiments, the method includes generating a second signal toadjust a shape of delivered pulsed power, the second signal correlatedto the data to minimize an amplitude difference between a peak of apulse and a substantially stable portion of the pulse. In someembodiments, the method includes correlating the second signal to a timedelay measured between a voltage source receiving a set point and avoltage to power converter outputting power. In some embodiments, themethod includes correlating the signal to the data to minimize a powerdifference between a power set point and a substantially stable portionof a pulse.

The invention, in another aspect, features a method of power delivery.The method includes delivering power from a power amplifier in acontinuous-wave mode to a load. The method also includes measuring powerdelivered to the load. The method also includes generating a signalindicative of the power delivered using a feedback loop to control theamplitude of the power delivered, the signal corresponding to a powercontrol algorithm. The method also includes adjusting a single variablein the algorithm to deliver pulsed power to the load via the samefeedback loop.

In some embodiments, the method includes activating a switch in thefeedback loop based on an input correlated to the single variable, theswitch in electrical communication with a power amplifier. In someembodiments, the method includes activating a switch in the feedbackloop based on an input corresponding to the single variable, the switchin electrical communication with a power amplifier. In some embodiments,the method includes filtering the data to provide a substantially stablepower measurement.

In some embodiments, the method includes providing the signal as aninput to a voltage source, the voltage source providing a voltage to avoltage to power converter. In some embodiments, the method includescorrelating the signal to a duty cycle input of the voltage source. Insome embodiments, the method includes calculating a power offset betweena power set point and the delivered power.

In some embodiments, the method includes measuring the delivered powerto obtain data. The method can include generating a second signal toadjust a shape of delivered pulsed power, the second signal correlatedto the data to minimize an amplitude difference between a peak of apulse and a substantially stable portion of the pulse. The method caninclude correlating the second signal to a time delay measured between avoltage source receiving a set point and a voltage to power converteroutputting power. In some embodiments, the method includes correlatingthe signal to the data to minimize a power difference between a powerset point and a substantially stable portion of a pulse.

The invention, in another aspect, features a system for deliveringpulsed or continuous-wave RF power to a load. The system includes avoltage to power converter coupled to an output of a voltage source, thevoltage to power converter adapted to generate the pulsed RF power orthe continuous-wave RF power. The system also includes a RF poweramplifier coupled to an output of the voltage to power converter, the RFpower amplifier adapted to deliver RF power to the load. The system alsoincludes a pulse shape control loop coupled to an output of the RF poweramplifier and a first input of the voltage source, the pulse shapecontrol loop adapted to minimize an amplitude difference between a peakof the pulsed power and a substantially stable portion of the pulsedpower, the pulse shape control loop adapted to operate when the pulsedRF power is in a first mode. The system also includes a power set pointcontrol loop coupled to the output of the RF power amplifier and asecond input of the voltage source, the power set point control loopadapted to minimize a power difference between a RF power set point andthe RF power delivered to the load.

In some embodiments, the power set point control loop is coupled to anoutput of the voltage source. In some embodiments, the power set pointcontrol loop includes a voltage offset circuit, the voltage offsetcircuit configured to measure a voltage offset between a voltage outputfrom the voltage source and a voltage setpoint from the power set pointcontrol loop.

In some embodiments, the power set point control loop includes a switchin electrical communication with the output of the RF power amplifier.The switch can have a switching frequency correlated to a pulsingfrequency of the pulsed RF power. In some embodiments, the systemincludes a matching network coupled to an output of the voltage to powerconverter and an input of the load. In some embodiments, the power setpoint control loop includes an output conditioning module coupled to thesecond input of the voltage source and the pulse set point control loop,the output conditioning module providing a duty cycle input to thevoltage source. The voltage source can be a buck regulator. In someembodiments, the power set point control loop includes adigital-to-analog converter.

The invention, in another aspect, features a system for deliveringpulsed or continuous-wave RF power to a load. The system includes avoltage to power converter coupled to an output of a voltage source, thevoltage to power converter adapted to produce the pulsed RF power or thecontinuous-wave RF power. The system also includes a RF power amplifiercoupled to an output of the voltage to power converter, the RF poweramplifier adapted to deliver RF power to the load. The system alsoincludes a first control circuit coupled to an output of the RF poweramplifier and a current set point output. The system also includes asecond control circuit coupled to an input of the voltage source and anoutput of the voltage source, the second control circuit in electricalcommunication with the current set point output. The first and secondcontrol circuits, in combination, are adapted to minimize a powerdifference between a RF power set point and the RF power delivered tothe load.

In some embodiments, the system includes a third control circuit coupledto the output of the voltage source and a voltage set point output ofthe second control circuit. In some embodiments, the system includes thefirst control circuit includes a switch in electrical communication withthe output of the RF power amplifier. In some embodiments, the systemincludes at least one filter in electrical communication with the switchand the output of the RF power amplifier. In some embodiments, the atleast one filter is adapted to provide a substantially stable powermeasurement.

In some embodiments, the system includes at least one feed-forward inputcoupled to the second control circuit. The at least one feed-forwardinput can include a voltage set point input. The at least onefeed-forward input can include a current set point input. In someembodiments, the second circuit includes a conditioning module, theconditioning module providing a duty cycle input to the voltage source.In some embodiments, the system includes a pulse shape control loopcoupled to an output of the RF power amplifier and a second input of thevoltage source, the pulse shape control loop adapted to minimize anamplitude difference between a peak of the pulsed power and asubstantially stable portion of the pulsed power, the pulse shapecontrol loop adapted to operate when the pulsed RF power is in a firstmode.

The invention, in another aspect, features a method of synchronizingpower delivery systems. The method includes generating a master pulsedpower from a master power delivery system. The method also includesgenerating a synchronizing pulse signal, the synchronizing pulse signalhaving a first frequency correlated to a pulse frequency of the masterpulsed power. The method also includes generating a slave pulsed powerfrom a slave power delivery system. The method also includessynchronizing the slave pulsed power with the synchronizing pulsesignal.

In some embodiments, the synchronizing step includes calculating asecond frequency of the slave pulsed power based on the first frequencyof the synchronizing pulse signal. In some embodiments, the calculatingstep includes measuring a time period between a falling edge and arising edge of the synchronization signal.

In some embodiments, the method includes calculating the secondfrequency of the slave pulsed power based on a falling edge of thesynchronizing pulse signal. In some embodiments, the method includescalculating the second frequency of the slave pulsed power based on arising edge of the synchronizing pulse signal. In some embodiments, themethod includes delaying a phase of the slave pulsed power relative tothe master pulsed power.

In some embodiments, the method includes receiving the synchronizingpulse signal from the master power delivery system. In some embodiments,the method includes receiving the synchronizing pulse signal from anexternal signal generator.

The invention, in another aspect, features a system for synchronizingpower delivery systems. The system includes a master power deliverysystem adapted to generate a master pulsed power. The system alsoincludes an external signal generator in electrical communication withthe master power delivery system. The system also includes a slave powerdelivery system in electrical communication with the external signalgenerator, wherein the slave power delivery system generates a slavepulsed power having a frequency correlated to a synchronization signalgenerated by the external signal generator.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, feature and advantages of theinvention, as well as the invention itself, will be more fullyunderstood from the following illustrative description, when readtogether with the accompanying drawings which are not necessarily toscale.

FIG. 1 is a schematic illustration of an RF power delivery system,according to an illustrative embodiment of the invention.

FIG. 2 is a schematic illustration of an RF power delivery system,according to an illustrative embodiment of the invention.

FIG. 3 is a graphical representation of an RF power signal varying frompulse to pulse, according to an illustrative embodiment of theinvention.

FIG. 4 is a schematic illustration of an RF power delivery system,according to an illustrative embodiment of the invention.

FIG. 5A is a schematic illustration of a master-slave RF power deliverysystem, according to an illustrative embodiment of the invention.

FIG. 5B is a graphical representation of synchronization of the slave RFpower delivery system of FIG. 5A to the master RF power delivery systemof FIG. 5A, according to an illustrative embodiment of the invention.

FIG. 6A is a schematic illustration of a master-slave RF power deliverysystem with an external trigger, according to an illustrative embodimentof the invention.

FIG. 6B is a graphical representation of synchronization of the slave RFpower delivery system of FIG. 6A to the master RF power delivery systemof FIG. 6A, according to an illustrative embodiment of the invention.

FIG. 6C is a graphical representation of synchronization of the slave RFpower delivery system of FIG. 6A to the master RF power delivery systemof FIG. 6A, according to another illustrative embodiment of theinvention.

FIG. 7 is a graphical illustration of synchronizing pulses in amaster-slave RF power delivery system, according to an illustrativeembodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 is a schematic illustration of an RF power delivery system 100,according to an illustrative embodiment of the invention. The system 100includes a voltage source 104 electrically coupled to a voltage to powerconverter 108. The voltage source 104 provides a DC voltage signal 106to the voltage to power converter 108. In some embodiments, the voltagesource 104 is a buck regulator. A buck regulator receives an unregulatedinput voltage and produces a lower, regulated output voltage.

The voltage to power converter 108 creates a DC power signal 110 (e.g.,a pulsed signal or a continuous wave signal) based on the DC voltagesignal 106 from the voltage source 104. The voltage to power converter108 outputs a pulsed or continuous wave signal based on properties of asynchronization signal 188 provided to the voltage to power converter108. If the synchronization signal 188 is a pulse signal (as shown), theDC power signal 110 output by the voltage to power converter 108 ispulses of DC power having the same frequency and period as the pulses ofthe synchronization signal 188. If, however, the synchronization signal188 is a continuous-wave signal (not shown), the DC power signal 110output by the voltage to power converter 108 is a continuous-wave DCpower signal.

The voltage to power converter 108 is electrically coupled to a poweramplifier 112 (e.g., an RF power amplifier). The voltage to powerconverter 108 provides the DC power signal 110 to the power amplifier112. The power amplifier 112 outputs an RF power signal 114 based on theDC power signal 110 received from the voltage to power converter 108.The power amplifier 112 can output the RF power signal with the sameproperties (e.g., pulses or continuous wave) as the properties of the DCpower signal or with different properties. In some embodiments, thepower amplifier 112 outputs an RF power signal 114 with properties thatare selected by an operator (or specified by a process controller) thatis desired for load 124.

The operating radio frequency of the power amplifier 112 can be manually(open-loop) or automatically (closed-loop) tuned to a specificfrequency. In either case, an operator provides a minimum and maximumallowable frequency limits (e.g., ±5% of center frequency 13.56 MHz) tothe control system 192 or power amplifier 112. In some embodiments, theminimum and maximum frequency limits are based on the characteristics ofthe load to, for example, maximize power transfer from the poweramplifier 112 to the load 124. In another embodiment, when operating thesystem in a pulsed operating mode, the operator specifies the pulsingfrequency and duty cycle to the control system 192. The desired valuesfor the pulsing frequency and duty cycle also are based on thecharacteristics of the load. In some embodiments, the power amplifier112 outputs an RF power signal 114 at frequencies between about 400 kHzand about 200 MHz. Typical RF Frequencies used in scientific, industrialand medical applications are approximately 2 MHz, 13.56 MHz, and 27 MHz.

The RF power amplifier signal 114 output by the power amplifier 112 canbe transitioned from a continuous-wave mode to a pulsed mode bytransitioning the synchronization signal 188 from a continuous-wavesignal to a pulsed signal. By transitioning from, for example, acontinuous-wave signal to a pulsed signal by adjusting a single variable(i.e., synchronization signal 188) in the power control algorithm (EQN.5, described below), the power control algorithm transitions thedelivered power from the continuous-wave mode to the pulsed mode.Likewise, the RF power signal 114 output by the power amplifier 112 canbe transitioned from a pulsed mode to a continuous-wave mode bytransitioning the synchronization signal 188 from a pulsed mode (shown)to a continuous-wave signal.

The power amplifier 112 outputs the RF power signal 114 to an optionalmatching network 120. In one embodiment, a power amplifier is used thathas the following nominal operating levels: 300 volt (RMS); 12 amps(RMS) and 3.5 kW. The matching network 120 is used in some embodimentsof the invention to match the impedance between the power amplifier 112and the load 124. It is desirable to match the impedance between thepower amplifier 112 and the load 124 to minimize the RF power that wouldotherwise be reflected back into the power amplifier from the load 124.The matching network 120 outputs a modified RF power signal 114′ inresponse to the RF power signal received from the power amplifier 112.In some embodiments, an estimate (or measured value) of the powerdissipated in the matching network 120 is used to calibrate the systemand modify the output of the power amplifier 112 to insure that the load124 receives the desired power.

The modified RF power signal 114′ is provided to the load 124 (e.g., aplasma processing chamber used to process semiconductor wafers). In someembodiments, properties (e.g., impedance) of the load 124 vary duringoperation. Properties of the load 124 may vary based on changes in, forexample, process conditions in a plasma chamber (e.g., gas flow rate,gas composition, and chamber pressure) and properties associated withthe RF power delivered to the load (e.g., peak RF power, RF pulsefrequency, RF pulse width/duty cycle).

The RF power delivery system 100 also includes a control system 192. Thepower amplifier 112 is in electrical communication with the componentsof the control system 192. The control system 192 provides a feedbackloop 198 used to control operation of the various components (e.g.,voltage source 104, voltage to power converter 108 and power amplifier112) of the RF power delivery system. The control system 192 includes ananalog compensation network 128 electrically coupled to the voltagesource 104 and an output conditioning module 132. The outputconditioning module 132 provides a control signal 134 (e.g., a pulsewidth modulated control signal or duty cycle input) to the voltagesource 104 that controls the output of the voltage source 104.

The control system 192 also includes a first analog-to-digital (A/D)converter 136 a. The A/D converter 136 a is electrically coupled to theoutput of the voltage source 104. The control system 192 also includes asecond analog-to-digital (A/D) converter 136 b. The A/D converter 136 bis electrically coupled to the output of a probe 116. The probe 116 iselectrically coupled to the power amplifier 112 to measure properties(e.g., data for the RF power signal) of the RF power signal 114 outputby the power amplifier 112. In this embodiment, the probe 116 outputsthe voltage signal (V_(rf)) and current signal (I_(rf)), which aremeasures of the RF power signal 114. V_(rf) and I_(rf) have thefollowing form:

V _(rf) =V _(R) +jV _(I)   EQN. 1

I _(rf) =I _(R) +jI _(I)   EQN. 2

where V_(R) is the real component of the V_(rf) signal, V_(I) is theimaginary component of the V_(rf) signal, I_(R) is the real component ofthe I_(rf) signal, I_(I) is the imaginary component of the I_(rf)signal.

In one embodiment, the voltage signal (V_(rf)) and the current signal(I_(rf)) output by the probe 116 are both sinusoidal signals when the RFpower signal 114 is a sinusoidal signal. Exemplary probes 116 for use indifferent embodiments of the invention are the Model VI-Probe-4100 andVI-Probe-350 (MKS Instruments, Inc., Andover, Mass.).

The A/D converter 136 b samples the two signals (V_(rf) and I_(rf)) andoutputs digital signals [digital voltage signal (V_(rf-dig)) and digitalcurrent signal (I_(rf-dig))].

The digital voltage signal (V_(rf-dig)) and digital current signal(I_(rf-dig)) are provided to a digital signal processing module 196 toproduce a digital signal (P_(del) _(—) _(ON)) that is the output powerof the power amplifier 112. The processing module 196 includes a digitalmixer 152, a CIC filter module 156, a switch 160, an IIR filter module164 and a power computation module 168. The digital mixer 152 converts atime varying signal into the real and imaginary components of the signalat a specified frequency. The decomposition achieved by multiplying themeasured signal with a reference cosine and a reference negative sinewave of the fundamental frequency produces DC components and a doublefrequency sine wave. The DC component obtained by multiplying the cosinerepresents the real component and the DC component obtained bymultiplying the negative sine wave represents the imaginary component.The double frequency components are filtered out by the CIC filter.

The output of the A/D converter 136 b (V_(rf-dig) and I_(rf-dig)) isprovided to the mixer 152. The mixer 152 performs mathematicalcalculations with the digital voltage signal (V_(rf-dig)) and digitalcurrent signal (I_(rf-dig)) to produce the real and imaginary portionsof the digital voltage signal (V_(rf-dig)) and digital current signal(I_(rf-dig)) of the form:

V _(rf-dig)=(V _(R-dig)+2*ω)+j(V _(I-dig)+2*ω)   EQN. 3

I _(rf-dig)=(I _(R-dig)+2*ω)+j(I _(I-dig)+2*ω)   EQN. 4

where V_(R-dig) is the real component of the digital version of V_(rf),V_(I-dig) is the imaginary component of the digital version of V_(rf),I_(R-dig) is the real component of the digital version of I_(rf), andI_(I-dig) is the imaginary component of the digital version of IfI_(rf), and where each component of the digital signals has a componentequal to 2*ω, where ω is the sampling frequency of the A/D converter.These signals are then provided to the CIC filter module 156 to removethe 2*ω component of the signals.

In one embodiment, the CIC filter module 156 is a low pass filter. Inone embodiment, the cutoff frequency of the low pass filter isapproximately 25 kHz. The CIC filter module 156 filters, for example,signal frequencies associated with the processing requirements of thesystem (e.g., typical frequencies used on scientific, industrial andmedical applications of approximately 2 MHz, 13.56 MHz and 27 MHz).

The output of the CIC filter module 156 is provided to the switch 160.The switch 160 is driven between open and closed positions by thesynchronization signal 188. The switch 160 is closed when the pulsemagnitude is 1 and the switch is closed when the pulse magnitude is 0.The output of the switch 160 is provided to the IIR filter module 164.

When the switch 160 is in the closed position, the current value of theDC signal is provided to the IIR filter module 164. When the switch 160is in the open position, the previous value of the DC signal is providedto the IIR filter module 164. The IIR filter module 164 is typically alow pass filter used to smooth the signals that are provided to thepower computation module 168. The IIR filter module 164 typicallysmooths noise/high frequency components that would otherwise be presentdue to the switch 160 being cycled between open and closed positions.The CIC filter module 156 and IIR filter module 164 filter the signalsin the digital signal processing module 196 of the feedback loop 198 toprovide a stable (the term which includes substantially stable) powermeasurement (digital signal 178). The output of the IIR filter module164 is provided to the power computation module 168. The powercomputation module 168 calculates the power based on the following powercontrol algorithm:

P _(del) _(—) _(ON) =V _(R-dig) I _(R-dig) +V _(I-dig) I _(I-dig)   EQN.5

The power computation module 168 outputs the digital signal 178 (P_(del)_(—) _(ON)). The signal 178 is the delivered power (power delivered tothe load 124). An operator or processor (not shown) provides a powersetpoint signal 184 (P_(sp)) to the RF power delivery system 100 whichis the RF power signal desired to be provided to the load 124. In someembodiments, a mathematical model of the desired operation of the systemis implemented on the processor to produce the power setpoint signal184. A summation module 180 c calculates a power offset, the differencebetween the power setpoint signal 184 and the output of the powercomputation module 168 (error e), based on the following:

e=P _(sp) −P _(del) _(—) _(ON)   EQN. 6

If the difference between the power setpoint signal 184 and the outputof the power computation module 168 is zero, the power amplifier 112 isproviding the desired RF power signal to the load 124. If the differenceis not zero, the system works to reduce the difference (error e).

The RF power delivery system 100 includes a first controller module 144that receives the output of the summation module 180 c (i.e., thedifference between the power setpoint signal 184 and the output 170 ofthe power computation module 168). The controller module 144 attempts toreduce the error between a measured process variable (i.e., output ofpower computation module 168) and a desired setpoint (i.e., powersetpoint 184) by calculating and then outputting a corrective actionthat can adjust the process accordingly.

In one embodiment, the controller module 144 is aproportional-integral-derivative (PID) controller module. Theproportional value determines the reaction of the controller 144 to thecurrent error, the integral value determines the reaction of thecontroller 144 based on the sum of recent errors, and the derivativevalue determines the reaction of the controller 144 based on the rate atwhich the error has been changing. The weighted sum of these threeactions is used to adjust the process via a control element based on thefollowing:

$\begin{matrix}{V_{control} = {{k_{p}e} + {k_{i}{\int{e{\tau}}}} + {k_{d}\frac{e}{t}}}} & {{EQN}.\mspace{14mu} 7}\end{matrix}$

where k_(p) is the value of the scalar constant for the proportionalcomponent of the PID control algorithm, k_(i) is the value of the scalarconstant for the integral component of the PID control algorithm, k_(d)is the value of the scalar constant for the derivative component of thePID control algorithm, and e is the error calculated in EQN. 6.

In this embodiment of the invention, the controller 144 outputs a signalthat is ultimately provided to the output conditioning module 132. Theoutput conditioning module 132 controls operation of the voltage source104 which in turn ultimately controls the power output by the poweramplifier 112. By tuning three constants in the PID controlleralgorithm, the controller can provide control action designed forspecific process requirements. The response of the controller can bedescribed in terms of the responsiveness of the controller to an error,the degree to which the controller overshoots the setpoint and thedegree of system oscillation. Alternative controller types (e.g.,state-space controllers, adaptive controllers, fuzzy-logic controller)can be used in alternative embodiments of the invention.

The output (V_(control)) of the controller 144 is combined (e.g.,summed) with a first feed-forward signal 172 with summing module 180 bto produce a voltage setpoint signal (V_(sp)). The first feed-forwardsignal 172 is typically generated using a mathematical model of thedesired operation of the system 100. In some embodiments, the firstfeed-forward signal 172 varies as a function of time (t). In someembodiments, the first feed-forward signal 172 is generated by anoperator. A feed-forward signal is typically used to ensure fasterconvergence to a given setpoint based on system information andparameters. In addition, a nonlinear feed-forward signal may be used inconjunction with a linear feedback function (e.g., PID control) toachieve fast control in a nonlinear system.

A summation module 180d calculates the difference between the voltagesetpoint signal (V_(sp)) and the output of an A/D converter 136 a. A/Dconverter 136 a samples the output of the voltage source 104 andproduces a digital version of the voltage source's 104 output(V_(buck)). Summation module 180 d calculates the difference (errore_(v)) between the voltage setpoint signal (V_(sp)) and V_(buck) basedon the following:

e _(v) =V _(sp) −V _(buck)   EQN. 8

If the difference between the voltage setpoint signal (V_(sp)) andV_(buck) is zero, the power amplifier 112 is providing the desired RFpower signal to the load 124. If the difference is not zero, the systemworks to reduce the difference (error e_(v)).

The RF power delivery system 100 also includes a second controllermodule 148 that receives the output of the summation module 180 d (i.e.,the difference between the voltage setpoint signal (V_(sp)) andV_(buck))). The controller module 148 attempts to correct the errorbetween a measured process variable (i.e., output of voltage source 104)and a desired setpoint (i.e., voltage setpoint V_(sp)) by calculatingand then outputting a corrective action that can adjust the processaccordingly.

In one embodiment, the controller module 148 is aproportional-integral-derivative (PID) controller module. Theproportional value determines the reaction of the controller 148 to thecurrent error, the integral value determines the reaction of thecontroller 148 based on the sum of recent errors, and the derivativevalue determines the reaction of the controller 148 based on the rate atwhich the error has been changing. The weighted sum of these threeactions is used to adjust the process via a control element based on thefollowing

$\begin{matrix}{I_{control} = {{k_{pv}e_{v}} + {k_{vi}{\int{e_{v}{\tau}}}} + {k_{dv}\frac{e_{v}}{t}}}} & {{EQN}.\mspace{14mu} 9}\end{matrix}$

where k_(pv) is the value of the constant for the proportional componentof the PID control algorithm, k_(iv) is the value of the constant forthe integral component of the PID control algorithm, k_(dv) is the valueof the constant for the derivative component of the PID controlalgorithm, and e_(v) is the error calculated in EQN. 8.

In this embodiment of the invention, the controller 148 outputs a signalthat is ultimately provided to the output conditioning module 132. Theoutput conditioning module 132 controls operation of the voltage source104 which in turn ultimately controls the power output by the poweramplifier 112. By tuning three constants in the PID controlleralgorithm, the controller can provide control action designed forspecific process requirements. The response of the controller can bedescribed in terms of the responsiveness of the controller to an error,the degree to which the controller overshoots the setpoint and thedegree of system oscillation. Alternative controller types (e.g.,state-space controllers, adaptive controllers, fuzzy-logic controller)can be used in alternative embodiments of the invention.

The output of the controller 148 is combined (e.g., summed) with asecond feed-forward signal 176 with summing module 180 a to produce acurrent setpoint signal (I_(sp)). The second feed-forward signal 176 istypically generated using a mathematical model of the desired operationof the system 100. In some embodiments, the second feed-forward signal176 varies as a function of time (t). In some embodiments, the secondfeed-forward signal 176 is generated by an operator.

The current setpoint signal (I_(sp)) is provided to a digital to analogconverter 140 which produces an analog signal version of the currentsetpoint signal (I_(sp)). The analog signal version of the of thecurrent setpoint signal (I_(sp)) is provided to an analog circuitcompensation network 128. The analog circuit compensation network 128also receives a signal (I_(meas)) that is the measured current from thevoltage source 104. In this embodiment, the analog circuit compensationnetwork 128 is a lead-lag compensation network that increases the phasemargin in the system and provides a signal to the output conditioningmodule 132. As discussed previously herein, the output conditioningmodule 132 provides a control signal (e.g., a pulse width modulatedcontrol signal) to the voltage source 104 that controls the output ofthe voltage source 104.

FIG. 2 is a schematic illustration of an RF power delivery system 200,according to an illustrative embodiment of the invention. The system 200includes a voltage source 204 electrically coupled to a voltage to powerconverter 208. The voltage source 204 provides a DC voltage signal 207to the voltage to power converter 208. In some embodiments, the voltagesource 204 is a buck regulator. A buck regulator receives an unregulatedinput voltage and produces a lower regulated output voltage. The voltageto power converter 208 creates a DC power signal 211 (e.g., a pulsedsignal or a continuous wave signal) based on the DC voltage signal 207from the voltage source 204. The voltage to power converter 208 outputsa pulsed or continuous wave signal based on properties of asynchronization signal 288 provided to the voltage to power converter208. If the synchronization signal 288 is a pulse signal (as shown), theDC power signal 211 output by the voltage to power converter 208 ispulses of DC power having the same frequency and period as the pulses ofthe synchronization signal 288. If, however, the synchronization signal288 is a continuous wave signal (not shown), the DC power signal 211output by the voltage to power converter 208 is a continuous wave DCpower signal.

The voltage to power converter 208 is electrically coupled to a poweramplifier 212 (e.g., an RF power amplifier). The voltage to powerconverter 208 provides the DC power signal 211 to the power amplifier212. The power amplifier 212 outputs an RF power signal 213 based on theDC power signal 211 received from the voltage to power converter 208.The power amplifier 212 can output the RF power signal 213 with the sameproperties (e.g., pulses or continuous wave) as the properties of the DCpower signal or with different properties. In some embodiments, thepower amplifier 212 outputs an RF power signal 213 that is selected byan operator (or specified by a process controller) that is desired forload 224. In some embodiments, the power amplifier 212 outputs an RFpower signal at frequencies between about 400 kHz and about 200 MHz.Typical RF Frequencies used in scientific, industrial and medicalapplications are approximately 2 MHz, 13.56 MHz, and 27 MHz.

The RF power amplifier signal 213 output by the power amplifier 212 canbe transitioned from a continuous-wave mode to a pulsed mode bytransitioning the synchronization signal 288 from a continuous-wavesignal to a pulsed signal. By transitioning from, for example, acontinuous-wave signal to a pulsed signal, by adjusting a singlevariable (i.e., synchronization signal 288) in the power controlalgorithm (EQN. 13, described below), the power control algorithmtransitions the delivered power from the continuous-wave mode to thepulsed mode. Likewise, the RF power signal 213 output by the poweramplifier 212 can be transitioned from a pulsed mode to acontinuous-wave mode by transitioning the synchronization signal 288from a pulsed mode (shown) to a continuous-wave signal.

The power amplifier 212 outputs the RF power signal 213 to an optionalmatching network 220. The matching network 220 is used in someembodiments of the invention to match the impedance between the poweramplifier 212 and the load 224. It is desirable to match the impedancebetween the power amplifier 212 and the load 224 to minimize the RFpower that would otherwise be reflected back into the power amplifierfrom the load 224. The matching network 220 outputs a modified RF powersignal 213′ in response to the RF power signal 213 received from thepower amplifier 212.

The modified RF power signal 113′ is provided to the load 224 (e.g., aplasma processing chamber used to process semiconductor wafers). In someembodiments, properties (e.g., impedance) of the load 224 vary duringoperation. Properties of the load 224 may vary based on changes in, forexample, process conditions in a plasma chamber (e.g., gas flow rate,gas composition, and chamber pressure) and properties associated withthe RF power delivered to the load (e.g., peak RF power, RF pulsefrequency, RF pulse width/duty cycle).

The RF power delivery system 200 also includes a control system 292. Thepower amplifier 212 is in electrical communication with the controlsystem 292. The control system 292 provides a feedback loop 298 used tocontrol operation of various components (e.g., voltage source 204,voltage to power converter 208 and power amplifier 212) of the RF powerdelivery system 200. The control system 292 includes an analogcompensation network 228 electrically coupled to the voltage source 204and an output conditioning module 232. The output conditioning module232 provides a control signal (e.g., a pulse width modulated controlsignal or duty cycle input) to the voltage source 204 that controls theoutput of the voltage source 204.

The control system 292 also includes a first analog to digital (A/D)converter 236 a. The A/D converter 236 a is electrically coupled to theoutput of the voltage source 204. The control system 292 also includes asecond analog to digital (A/D) converter 236 b. The A/D converter 236 bis electrically coupled to the output of a probe 216. The probe 216 iselectrically coupled to the power amplifier 212 to measure properties(e.g., data for the RF power signal) of the RF power signal output bythe power amplifier 212. In this embodiment, the probe 216 outputs thevoltage signal (V_(rf)) and current signal (I_(rf)) of the RF powersignal, which are measures of the RF power signal 213. V_(rf) and I_(rf)have the following form:

V _(rf) =V _(R) +jV _(I)   EQN. 9

I _(rf) =I _(R) +jI _(I)   EQN. 10

where V_(R) is the real component of the V_(rf) signal, V_(I) is theimaginary component of the V_(rf) signal, I_(R) is the real component ofthe I_(rf) signal, I_(I) is the imaginary component of the I_(rf)signal.

In one embodiment, the voltage signal (V_(rf)) and the current signal(I_(rf)) output by the probe 216 are both sinusoidal signals. Exemplaryprobes 216 for use in different embodiments of the invention are theModel VI-Probe-4100 and VI-Probe-350 (MKS Instruments, Inc., Andover,Mass.). The A/D converter 236 b samples the two signals (V_(rf) andI_(rf)) and outputs digital signals [digital voltage signal (V_(rf-dig))and digital current signal (I_(rf-dig))].

The digital voltage signal (V_(rf-dig)) and digital current signal(I_(rf-dig)) are provided to a digital signal processing module 296 toproduce a digital signal (P_(del)) that is the output power of the poweramplifier 212. The processing module 296 includes a digital mixer 252, aCIC filter module 256, and a power computation module 268. The output ofthe A/D converter 236 b (V_(rf-dig) and I_(rf-dig)) is provided to themixer 252. The mixer 252 performs mathematical calculations with thedigital voltage signal (V_(rf-dig)) and digital current signal(I_(rf-dig)) to produce the real and imaginary portions of the digitalvoltage signal (V_(rf-dig)) and digital current signal (I_(rf-dig)) ofthe form:

V _(rf-dig)=(V _(R-dig)+2*ω)+j(V _(I-dig)+2*ω)   EQN. 11

I _(rf-dig)=(I _(R-dig)+2*ω)+j(I _(I-dig)+2*ω)   EQN. 12

where V_(R-dig) is the real component of the digital version of V_(rf),V_(I-dig) is the imaginary component of the digital version of V_(rf),I_(R-dig) is the real component of the digital version of I_(rf), andI_(I-dig) is the imaginary component of the digital version of I_(rf),and where each component of the digital signals has a component equal to2*ω, where ω is the sampling frequency of the A/D converter. Thesesignals are then provided to the CIC filter module 256 to remove the 2*ωcomponent of the signals. The DC signal output by the CIC filter module256 is provided to the power computation module 268. The powercomputation module calculates the power based on the following powercontrol algorithm:

P _(del) =V _(R-dig) I _(R-dig) +V _(I-dig) I _(I-dig)   EQN. 13

The power computation module 268 outputs the digital signal 278(P_(del)). The signal 278 is the delivered power (i.e., power deliveredto the load 224). An operator or processor (not shown) provides a powersetpoint signal 284 (P_(sp)) to the RF power delivery system 200 whichis the RF power signal desired to be provided to the load 224. In someembodiments, a mathematical model of the desired operation of the systemis implemented on the processor to produce the power setpoint signal284.

FIG. 3 is a graphical representation of a plot 300 of the digital signal302 which is the digital signal 278 (P_(del)) of FIG. 2. Referring toFIG. 3, the digital signal 278 varies from pulse to pulse as a result ofapplying a method for controlling the delivery of power, according to anillustrative embodiment of the invention described in FIG. 2. The Y-Axisof the plot 300 is the digital representation of the RF power signal 213output by the power amplifier 212. The X-Axis of the plot is time. Inthis embodiment, the plot 300 illustrates three pulses of power [304 a,304 b and 304 c (generally, 304)] output by the power amplifier 212. Itis desirable for each pulse 304 to have a constant value P_(sp) (powersetpoint). However, in practice, the pulses 304 are not ideal pulses andtherefore there is an error between the desired pulse and the actualpulses of power output by the power amplifier 212.

The system 200 corrects for the error between the desired pulse and theactual pulses of power output by the power amplifier 212. The error foreach pulse 304 is characterized by a first error component e₁ and asecond error component e₂. Error component e₁ is the error between thepower setpoint (P_(sp)) and the substantially stable (steady state)portion of the delivered power P_(del). The value for P_(del) used incalculating error component e₁ is the power at the end of the pulse.Error e₁(n) is the first error component for the n^(th) pulse and isreferred to as power offset error (e₁) in FIG. 2. Error component e₂ isthe error between the peak power delivered for a pulse (P_(del) _(—)_(peak)) and the substantially stable (steady state) portion of thedelivered power P_(del). Error e₂(n) is the second error component forthe n^(th) pulse and is referred to as pulse shape error (e₂) in FIG. 2.In operation, the power delivery system 200 reduces the errors e₁ and e₂from a first pulse (e.g., pulse 304 a) to a subsequent, second pulse(e.g., pulse. 304 b). Similarly, the power delivery system 200 reducesthe errors e₁ and e₂ between each successive set of pulses (e.g., afirst pulse 304 b to the subsequent second pulse 304 c).

A first pulse of the synchronization signal 288 is provided to thevoltage to power converter 208. The voltage to power converter 208provides a DC power pulse (DC power signal 211) to the power amplifier212. The power amplifier 212 outputs a first pulse of power (RF powersignal 213) to the matching network 220. The probe 216 measures thepulse of power (RF power signal 213) and outputs the voltage signal(V_(rf)) and current signal (I_(rf)) of the RF power signal to the A/Dconverter 236 b, as described previously herein. The power computationmodule 268 receives the output of the A/D converter 236 b and outputsthe digital signal (P_(del)), as described previously herein.

The power offset error (e₁) is provided to a power offset adaptivecontrol loop module 214. The power setpoint P_(sp) also is provided tothe module 214. The module 214 calculates a power offset signal(P_(offset)) based on the following adaptive algorithm:

$\begin{matrix}{\frac{\left( P_{offset} \right)}{t} = {k_{offset}\left( {P_{sp} - P_{del\_ end}} \right)}} & {{EQN}.\mspace{14mu} 14}\end{matrix}$

where k_(offset) is a scalar constant chosen by an operator to achievethe desired pulse power. Summation module 280 c sums P_(offset) with anoutput of the duty cycle module 210, and subtracts P_(del) from thissum. The output (error e) of the summation module 280 c is determinedbased on the following:

e=P _(sp) ·D−P _(del)   EQN. 15

where D is the duty cycle set by the duty cycle module 210. The outputof the summation module 280 c is provided to the controller 244.

Controller 244 attempts to reduce the error between a measured processvariable (i.e., output P_(del) of the power computation module 268) andthe sum of the power setpoint (P_(sp)) and output of the power offsetadaptive control module 214.

In one embodiment, the controller module 244 is aproportional-integral-derivative (PID) controller module. Theproportional value determines the reaction of the controller 244 to thecurrent error, the integral value determines the reaction of thecontroller 244 based on the sum of recent errors, and the derivativevalue determines the reaction of the controller 244 based on the rate atwhich the error has been changing. The weighted sum of these threeactions is used to adjust the process via a control element based on thefollowing:

$\begin{matrix}{V_{control} = {{k_{p}e} + {k_{i}{\int{e{\tau}}}} + {k_{d}\frac{e}{t}}}} & {{EQN}.\mspace{14mu} 16}\end{matrix}$

where k_(p) is the value of the scalar constant for the proportionalcomponent of the PID control algorithm, k_(i) is the value of the scalarconstant for the integral component of the PID control algorithm, k_(d)is the value of the scalar constant for the derivative component of thePID control algorithm, and e is the error calculated in EQN. 15.

In this embodiment of the invention, the controller 244 outputs a signalthat is ultimately provided to the output conditioning module 232. Theoutput conditioning module 232 controls operation of the voltage source204 which in turn ultimately controls the power output by the poweramplifier 212. By tuning three constants in the PID controlleralgorithm, the controller can provide control action designed forspecific process requirements. The response of the controller can bedescribed in terms of the responsiveness of the controller to an error,the degree to which the controller overshoots the setpoint and thedegree of system oscillation. Alternative controller types (e.g.,state-space controllers, adaptive controllers, fuzzy-logic controller)can be used in alternative embodiments of the invention.

The output (V_(control)) of the controller 244 is combined (e.g.,summed) with a first feed-forward signal 272 with summing module 280 bto produce a voltage setpoint signal (V_(sp)). The first feed-forwardsignal 272 is typically generated using a mathematical model of thedesired operation of the system 200. In some embodiments, the firstfeed-forward signal 272 varies as a function of time (t). In someembodiments, the first feed-forward signal 272 is generated by anoperator.

A summation module 280 d calculates the difference between the voltagesetpoint signal (V_(sp)) and the output of the A/D converter 236 a. A/Dconverter 236 a samples the output of the voltage source 204 andproduces a digital version of the voltage source's 204 output(V_(buck)). Summation module 280 d calculates the difference between thevoltage setpoint signal (V_(sp)) and V_(buck) based on the following:

e _(v) =V _(sp) −V _(buck)   EQN. 17

If the difference (error e_(v)) between the voltage setpoint signal(V_(sp)) and V_(buck) is zero, the power amplifier 212 is providing thedesired RF power signal to the load 224.

The RF power delivery system 200 also includes a second controllermodule 248 that receives the output of the summation module 180 d (i.e.,the difference between the voltage setpoint signal (V_(sp)) andV_(buck))). The controller module 248 attempts to correct the errorbetween a measured process variable (i.e., output of voltage source 204)and a desired setpoint (i.e., voltage setpoint V_(sp)) by calculatingand then outputting a corrective action that can adjust the processaccordingly.

In one embodiment, the controller module 248 is aproportional-integral-derivative (PID) controller module. Theproportional value determines the reaction of the controller 248 to thecurrent error, the integral value determines the reaction of thecontroller 248 based on the sum of recent errors, and the derivativevalue determines the reaction of the controller 248 based on the rate atwhich the error has been changing. The weighted sum of these threeactions is used to adjust the process via a control element based on thefollowing:

$\begin{matrix}{I_{control} = {{k_{pv}e_{v}} + {k_{vi}{\int{e_{v}{\tau}}}} + {k_{dv}\frac{e_{v}}{t}}}} & {{EQN}.\mspace{14mu} 18}\end{matrix}$

where k_(pv) is the value of the constant for the proportional componentof the PID control algorithm, k_(iv) is the value of the constant forthe integral component of the PID control algorithm, k_(dv) is the valueof the constant for the derivative component of the PID controlalgorithm, and e_(v) is the error determined with EQN. 17.

In this embodiment of the invention, the controller 248 outputs a signalthat is ultimately provided to the output conditioning module 232. Theoutput conditioning module 232 controls operation of the voltage source204 which in turn ultimately controls the power output by the poweramplifier 212. By tuning three constants in the PID controlleralgorithm, the controller can provide control action designed forspecific process requirements. The response of the controller can bedescribed in terms of the responsiveness of the controller to an error,the degree to which the controller overshoots the setpoint and thedegree of system oscillation. Alternative controller types (e.g.,state-space controllers, adaptive controllers, fuzzy-logic controller)can be used in alternative embodiments of the invention.

The output of the controller 248 is combined (e.g., summed) with asecond feed-forward signal 276 with summing module 280 a to produce acurrent setpoint signal (I_(sp)). The second feed-forward signal 276 istypically generated using a mathematical model of the desired operationof the system 200. In some embodiments, the second feed-forward signal276 varies as a function of time (t). In some embodiments, the secondfeed-forward signal 276 is generated by an operator.

The current setpoint signal (I_(sp)) is provided to a digital to analogconverter 240 which produces an analog signal version of the currentsetpoint signal (I_(sp)). The analog signal version of the of thecurrent setpoint signal (I_(sp)) is provided to an analog circuitcompensation network 228. The analog circuit compensation network 228also receives a signal (I_(meas)) that is the measured current from thevoltage source 204. In this embodiment, the analog circuit compensationnetwork 228 is a lead-lag compensation network that increases the phasemargin in the system and provides a signal to the output conditioningmodule 232. As discussed previously herein, the output conditioningmodule 232 provides a control signal (e.g., a pulse width modulatedcontrol signal) to the voltage source 204 that controls the output ofthe voltage source 204.

However, a buck delay adaptive control loop module 218 also affects theDC voltage signal 207 output by the voltage source 204. The buck delayadaptive control loop module 218 compensates for error e₂, which isdetermined using summation module 280 e based on the following (withreference to FIGS. 2 and 3):

e ₂ =P _(del) ⁻ _(end) −P _(del) _(—) _(peak)   EQN. 19

The error signal (pulse shape error e₂) is provided to the buck delayadaptive control loop module 218. The synchronization signal 288 also isprovided to the buck delay adaptive control loop module 218. The controlloop module 218 applies the following to compensate for a time delay(τ_(buck) _(—) _(dlye)):

$\begin{matrix}{\frac{\left( \tau_{buck\_ dlye} \right)}{t} = {- {k_{dly}\left( {P_{del\_ end} - P_{del\_ peak}} \right)}}} & {{EQN}.\mspace{14mu} 20}\end{matrix}$

where τ_(buck) _(—) _(dlye) is the time between the application of DCpower to the voltage source 204 and delivery of the desired magnitude ofRF power by the power amplifier 212, and k_(dly) is a scalar constantchosen by an operator to achieve the desired power.

FIG. 4 is a schematic illustration of an RF power delivery system 400,according to an illustrative embodiment of the invention. The system 400includes a voltage source 404 electrically coupled to a voltage to powerconverter 408. The voltage source 404 provides a voltage (e.g., a DCvoltage) to the voltage to power converter 408. In some embodiments, thevoltage source 404 is a buck regulator. The voltage to power converter408 creates a DC power signal (e.g., a pulsed signal or a continuouswave signal) based on the voltage from the voltage source 404.

The voltage to power converter 408 is electrically coupled to a poweramplifier 412 (e.g., an RF power amplifier). The voltage to powerconverter 408 provides the DC power signal to the power amplifier 412.The power amplifier 412 outputs an RF power signal 414 based on the DCpower signal received from the voltage to power converter 408. The poweramplifier 412 can output the RF power signal 414 with the sameproperties (e.g., pulses or continuous wave) as the properties of the DCpower signal or with different properties. In some embodiments, thepower amplifier 412 outputs an RF power signal 414 that is selected byan operator (or specified by a process controller) that is desired forload 424. In some embodiments, the power amplifier 412 outputs an RFpower signal at frequencies between about 400 kHz and about 200 MHz.Typical RF Frequencies used in scientific, industrial and medicalapplications are approximately 2 MHz, 13.56 MHz, and 27 MHz.

The power amplifier 412 outputs the RF power signal to an optionalmatching network 420. The matching network 420 is used in someembodiments of the invention to match the impedance between the poweramplifier 412 and the load 424. It is desirable to match the impedancebetween the power amplifier 412 and the load 424 to minimize the RFpower that would otherwise be reflected back into the power amplifierfrom the load 424. The matching network 420 outputs a modified RF powersignal in response to the RF power signal received from the poweramplifier 412.

The modified RF power signal is provided to the load 424 (e.g., a plasmaprocessing chamber used to process semiconductor wafers). In someembodiments, properties (e.g., impedance) of the load 424 vary duringoperation. Properties of the load 424 may vary based on changes in, forexample, process conditions in a plasma chamber (e.g., gas flow rate,gas composition, and chamber pressure) and properties associated withthe RF power delivered to the load (e.g., peak RF power, RF pulsefrequency, RF pulse width/duty cycle).

The RF power delivery system 400 also includes a control system 492. Thecontrol system 492 includes an analog compensation network 428electrically coupled to the voltage source 404 and an outputconditioning module 432. The output conditioning module 432 provides acontrol signal (e.g., a pulse width modulated control signal) to thevoltage source 404 that controls the output of the voltage source 404.

The control system 492 also includes an analog to digital (A/D)converter 436. The A/D converter 436 is electrically coupled to theoutput of a probe 416. The probe 416 is electrically coupled to thepower amplifier 412 to measure properties (e.g., data for the RF powersignal) of the RF power signal output by the power amplifier. In thisembodiment, the probe 416 outputs the voltage signal (V_(rf)) andcurrent signal (I_(rf)), which are measures of the RF power signal 414.

V_(rf) and I_(rf) have the following form:

V _(rf) =V _(R) +jV _(I)   EQN. 21

I _(rf) =I _(R) +jI _(I)   EQN. 22

where V_(R) is the real component of the V_(rf) signal, V_(I) is theimaginary component of the V_(rf) signal, I_(R) is the real component ofthe I_(rf) signal, I_(I) is the imaginary component of the I_(rf)signal.

In one embodiment, the voltage signal (V_(rf)) and the current signal(I_(rf)) output by the probe 416 are both sinusoidal signals. Exemplaryprobes 416 for use in different embodiments of the invention are theModel VI-Probe-4100 and VI-Probe-350 (MKS Instruments, Inc., Andover,Mass.). The A/D converter 436 samples the two signals (V_(rf) andI_(rf)) and outputs digital signals [digital voltage signal (V_(rf-dig))and digital current signal (I_(rf-dig))]. The digital voltage signal(V_(rf-dig)) and digital current signal (I_(rf-dig)) are provided to adigital signal processing module 496 to produce a digital signal(P_(del)) that is the output power of the power amplifier 412.

An operator or processor (not shown) provides a power setpoint signal484 (P_(sp)) to the RF power delivery system 400 which is the RF powersignal desired to be provided to the load 424. In some embodiments, amathematical model of the desired operation of the system is implementedon the processor to produce the power setpoint signal 484.

The RF power delivery system 400 also includes a first controller module450 that receives the P_(del) signal (from processing module 496) andthe P_(sp) signal (484). The controller module 450 attempts to correctthe error between a measured process variable (i.e., output ofprocessing module 496) and the desired setpoint (P_sp 484) bycalculating and then outputting a corrective action that can adjust theprocess accordingly. The controller module 450 outputs a DC currentreference signal to a D/A converter 440. The D/A converter outputs ananalog DC current reference signal (I_(ref)) to an analog compendationnetwork 428. The voltage source 404 provides a signal to the analogcompensation network 428 that is the DC current (I_(oc)) in the voltagesource 404. The analog compensation network 428 outputs a duty cyclesignal V_(duty) to an output conditioning module 432 based on the DCcurrent (I_(oc)) and the DC current reference signal (I_(ref)). Theoutput conditioning module 432 outputs a PWM signal to the voltagesource 404.

In one embodiment, the controller module 450 is aproportional-integral-derivative (PID) controller module, similarly aspreviously described herein with respect, to, for example FIGS. 1 and 2.The proportional value determines the reaction of the controller 450 tothe current error, the integral value determines the reaction of thecontroller 450 based on the sum of recent errors, and the derivativevalue determines the reaction of the controller 450 based on the rate atwhich the error has been changing. The weighted sum of these threeactions is used to adjust the process via a control element. The outputconditioning module 432 controls operation of the voltage source 404which in turn ultimately controls the power output by the poweramplifier 412. By tuning three constants in the PID controlleralgorithm, the controller can provide control action designed forspecific process requirements. The response of the controller can bedescribed in terms of the responsiveness of the controller to an error,the degree to which the controller overshoots the setpoint and thedegree of system oscillation. Alternative controller types (e.g.,state-space controllers, adaptive controllers, fuzzy-logic controller)can be used in alternative embodiments of the invention.

FIG. 5A is a schematic illustration of a master-slave RF power deliverysystem 500, according to an illustrative embodiment of the invention.The system 500 includes a master power delivery system 504 (e.g., RFpower delivery system 100 or 200 of FIGS. 1 and 2, respectively) thatgenerates RF power that is provided to load 508. The system 500 alsoincludes a plurality (m) of slave power delivery systems (e.g., aplurality of RF power delivery systems 100 or 200 of FIGS. 1 and 2,respectively), each coupled to the master power delivery system 504.

FIG. 5A depicts a first slave power supply 512 that generates an RFpower signal that is provided to load 516. FIG. 5A also depicts powerdelivery system # m (520) that provides RF power to load 524. FIG. 5B isa graphical representation of synchronization of power delivery system #m (520) to the master power delivery system 504. The master powerdelivery system 504 generates a synchronizing pulse signal 528(referring to FIG. 5A) that is provided to each of the (m) powerdelivery systems. The synchronizing pulse signal 528 (e.g., thesynchronization signal 188 of FIG. 1 and the synchronization signal 288of FIG. 2) is correlated to the frequency (f_(pulse)) of the pulsespower output by the master power delivery system 504 to the load 508.The system 500 applies a time delay φ_(sp(m)) to the synchronizing pulsesignal 528 and triggers the slave power delivery system 520 to generatea slave pulsed power 532 to be generated by the slave power deliverysystem 520, thereby synchronizing the slave pulsed power 532 with thesynchronizing pulse signal 528. The phase shift for each slave powerdelivery system is individually set/programmed by an operator. In someembodiments, the phase shift is the same for each slave power deliverysystem. The index m denotes the number of RF generator slave powerdelivery systems are connected to the master RF generator 504. Thepulsing duty cycle (dc(m)) is set by an operator and is often determinedbased on the load and desired operating conditions of the system.

FIG. 6A is a schematic illustration of a master-slave RF power deliverysystem 600, according to an illustrative embodiment of the invention.The system 600 includes a master power delivery system 604 (e.g., RFpower delivery system 100 or 200 of FIGS. 1 and 2, respectively) thatgenerates RF power that is provided to load 608. The system 600 alsoincludes a plurality (m) of slave power delivery systems (e.g., aplurality of RF power delivery systems 100 or 200 of FIGS. 1 and 2,respectively), each coupled to the master power delivery system 604.

FIG. 6A depicts a first slave power supply 612 that generates an RFpower signal that is provided to load 616. FIG. 6A also depicts powerdelivery system # m (620) that provides RF power to load 624. FIG. 6B isa graphical representation of synchronization of power delivery system #m (620) to the master power delivery system 604. An externalsynchronization trigger (e.g., pulse train) signal 628 is provided tothe master power delivery system 604 by, for example, an external signalgenerator that is in electrical communication with the master powerdelivery system. The external synchronization trigger signal 628 isprovided to each of the (m) power delivery systems. The master powerdelivery system 604 generates an RF power signal and delivers the RFpower signal to the load 608 based on the external synchronizationtrigger signal 628. Each of the (m) slave power delivery systemsgenerate RF power signals and deliver the RF power signals to respectiveloads based on the external synchronization trigger signal 628. Thesystem 600 applies a time delay φ_(sp(m)) to the synchronizing pulsesignal 628 and triggers the slave power delivery system 620 to generatea slave pulsed power 632 to be generated by the slave power deliverysystem 620, thereby synchronizing the slave pulsed power 632 with thesynchronizing pulse signal 628. The index m denotes the number of RFgenerator slave power delivery systems are connected to the master RFgenerator 604. The pulsing duty cycle (dc(m)) is set by an operator andis often determined based on the load and desired operating conditionsof the system.

FIG. 6C is a graphical representation of an alternative method forsynchronization of power delivery system # m (620) to the master powerdelivery system 604. The alternative method involves a single triggersignal that is used to trigger the power delivery systems to output RFpower to their respective loads. The external synchronization triggersignal 628 is provided to the master power delivery system 604 by, forexample, an external trigger source. The external synchronizationtrigger signal 628 is provided to each of the (m) power deliverysystems. The master power delivery system 604 generates an RF powersignal and delivers the RF power signal to the load 608 based on theexternal synchronization trigger signal 628. Each of the (m) slave powerdelivery systems generate RF power signals and deliver the RF powersignals to respective loads based on the external synchronizationtrigger signal 628. The system 600 applies a time delay φ_(sp(m)) to thesynchronizing pulse signal 628 and triggers the slave power deliverysystem 620 to generate a slave pulsed power 632 to be generated by theslave power delivery system 620, thereby synchronizing the slave pulsedpower 632 with the synchronizing pulse signal 628.

FIG. 7 is a graphical illustration of synchronizing pulses in amaster-slave RF power delivery system, according to an illustrativeembodiment of the invention. In this embodiment, signal 704 is the RFpower signal generated by a master power delivery system (e.g., RF powerdelivery system 504 of FIG. 5A). The RF power system generates asynchronization signal 708 based on the RF power signal 704. In thisembodiment, the synchronization signal 708 is the inverse of the RFpower delivery signal 704. The synchronization signal 708 is deliveredto a first and second slave power delivery system. The first slave powerdelivery system generates an RF power signal 712 having a time delay(slave_dly) and duty cycle that is specific for the first slave powerdelivery system. The second slave power delivery system generates an RFpower signal 716 having a time delay (slave_dly) and duty cycle that isspecific for the second slave power delivery system. The time delay andduty cycle for one slave power delivery system can be, but is notrequired to be, the same as the time delay and duty cycle of any otherslave power delivery system.

In some embodiments, synchronizing a slave power delivery system to asynchronization signal includes calculating a second frequency for theslave power delivery system based on the frequency of thesynchronization signal. In some embodiments, calculating the secondfrequency includes measuring the time period between a falling edge ofand rising edge of the synchronization signal.

Embodiments of the invention described herein are useful in providingpower to a plasma load having variable load impedance. Embodiments ofthe invention are capable of stabilizing a plasma over a wide range ofplasma conditions, including, for example, rapid changes in plasma gasspecies, rapid changes in plasma gas pressure and/or flow rate, andrapid changes in delivered power levels during plasma processing,without the onset of plasma instability or plasma drop out (i.e., lossof plasma ignition).

The plasma processing capabilities achieved using various embodiments ofthe invention are valuable in commercial plasma processing applicationsbecause they allow for faster plasma process transitions. Faster plasmaprocess transitions result in an increase in the throughput (and therebylower cost) of the process. The plasma processing capabilities alsoprovide a benefit to the manufacturing yield and process capability inplasma applications by improving the plasma process control (e.g.,process property repeatability within a specific workpiece or betweenworkpieces over time).

The technologies described herein and the plasma processing capabilityprovided, as described above, provides increased process throughput(e.g., lower cost per workpiece) and improved process control (e.g.,higher yield) in a variety of industrial and commercial applications,including: Plasma etch or reactive ion etch (RIE) of films or substratesin semiconductor manufacturing, solar cell manufacturing, or otherplasma etch industrial applications; Plasma-enhanced chemical vapordeposition (PECVD) of films in semiconductor manufacturing, solar cellmanufacturing, or other PECVD industrial applications; Ionized physicalvapor deposition (iPVD) of films in semiconductor manufacturing, solarcell manufacturing, or other iPVD industrial applications; and Atomiclayer deposition (ALD) of films in semiconductor manufacturing, solarcell manufacturing, or other ALD industrial applications.

In some embodiments, the technologies described herein provide a userwith the capability to pulse the RF power at high frequency and providesfor flexible synchronization of the source and bias RF power pulsing(e.g., flexible settings of relative pulse timing and duty cycle). Thetechnologies described herein and the plasma processing capabilityprovided enable, for example, continuous, independent variation ofseveral important plasma parameters (including electron density andtemperature, ion density and temperature, positive and negative ionfractions, etc.), which would allow more flexible optimization of plasmaprocesses than is available with purely CW RF power, without physicalmodification to the inside of the plasma processing chamber.

The technologies described herein and the plasma processing capabilityprovided also enable extended pressure/power operating regimes (notavailable with pure CW RF operation), higher etch and deposition rateswith lower average RF power, reduced heat flux and charging ofworkpiece, and independent adjustment of important plasma chemistrycomponents.

The technologies described herein and the plasma processing capabilityprovided provide lower electron temperature with approximately unchangedaverage plasma density, which allows reduction of electron bombardment,charging, and damage (such as “notching”, “micro-trenching”, or “etchpits”) to devices on substrates (workpieces), without reducingthroughput in plasma processing.

The technologies described herein and the plasma processing capabilityprovided also provide improved etch selectivity (differences in etchrate between the target film and the etch mask, sub-layers under thetarget film, or other materials exposed to the process) and anisotropy(the control of vertical sidewall angles in high aspect ratiostructures) by improving the adhesion of blocking polymers to verticalsidewalls and bottoms of structures during the off-pulse period andenabling independent control of the energy and number of ions bombardingthe substrate during the on-pulse period. This reduces the lateral etchrate by ions during the on-pulse period and improves etch selectivitybetween different materials on the workpiece, providing improved etchcontrol in a variety of applications, such as gate etch, trench etch,and metal etch plasma processes.

The technologies described herein and the plasma processing capabilityprovided also provide higher thin film deposition rate and improved filmmaterials properties in PECVD and ionized PVD (iPVD) processes byindependent control of electron energy & temperature, average ionenergy, ion energy distribution (IED), total ion flux, and reduced heatflux to the substrate.

With increasing workpiece sizes (e.g., wafer diameter in semiconductorfabrication, panel area in solar cell fabrication), achieving ormaintaining desirable uniformity across the workpiece of etch rate anddeposition rate in plasma processes is becoming more challenging.Furthermore, the etch rate, etch selectivity, anisotropy, the incidentalelectron charging/damage (such as “notching” and “micro-trenching”), andthe heat flux to the substrate are becoming more and more difficult tosimultaneously optimize. In particular, adequate aspect ratio controlacross the workpiece, especially with high aspect ratio structures, isbecoming increasingly difficult to achieve. RF pulsing, especiallyflexible synchronized pulsing of the RF source and RF bias generators,is well-known to enable independent, simultaneous optimization of theseconflicting plasma process requirements. For example synchronizedsource-bias pulsing is known to eliminate two important problems in etchprocesses, notching/micro-trenching damage and ARDE (Aspect RatioDependant Etching). Furthermore, it has been reported that, with highfrequency pulsing, the etch rate with very large area substrates (glasspanels) can be more than doubled while reducing the substrate processtemperature to less than 1200 C, relative to continuous RF processing.

Accordingly, it is therefore desirable to provide a user with thecapability to pulse the RF power at high frequency and also provideflexible synchronization of the source and bias RF power pulsing.Technologies described herein provide such improved plasma processingcontrol and are useful in various industrial and commercialapplications, including, for example: Plasma etch or reactive ion etch(RIE) of films or substrates in semiconductor manufacturing, solar cellmanufacturing, or other plasma etch industrial applications;Plasma-enhanced chemical vapor deposition (PECVD) of films insemiconductor manufacturing, solar cell manufacturing, or other PECVDindustrial applications; Ionized physical vapor deposition (iPVD) offilms in semiconductor manufacturing, solar cell manufacturing, or otheriPVD industrial applications; and Atomic layer deposition (ALD) of filmsin semiconductor manufacturing, solar cell manufacturing, or other ALDindustrial applications.

In some embodiments, the technology described herein provides thecapability to apply dual frequency RF bias power (i.e., adjustableamounts of power from either of two different RF generators withdifferent frequencies) to a workpiece in a plasma process. Thetechnologies described herein and the plasma processing capabilityprovided enable flexible, independent adjustment of average energy ofthe ion energy distribution (IED) in the plasma (by controlling thetotal combined power of the two bias frequencies) and the width of theIED (by adjustment of the ratio of the power applied from each of thetwo frequencies). This technique enables orthogonal control of these twoimportant parameters, independent of the plasma density, which iscontrolled by the source RF power & frequency, and the process gaspressure & flow settings. The technologies described herein and theplasma processing capability provided also provide improved control ofpolymer deposition, etch rate & selectivity, etch profile, and etch CDcontrol through flexible adjustment of average ion energy and ion energydistribution width.

The capability to independently control average ion energy and the widthof the IED would provide improved plasma processing control in, forexample, the following industrial and commercial applications: Plasmaetch or reactive ion etch (RIE) of films or substrates in semiconductormanufacturing, solar cell manufacturing, or other plasma etch industrialapplications; Plasma-enhanced chemical vapor deposition (PECVD) of filmsin semiconductor manufacturing, solar cell manufacturing, or other PECVDindustrial applications; Ionized physical vapor deposition (iPVD) offilms in semiconductor manufacturing, solar cell manufacturing, or otheriPVD industrial applications; and Atomic layer deposition (ALD) of filmsin semiconductor manufacturing, solar cell manufacturing, or other ALDindustrial applications.

Variations, modifications, and other implementations of what isdescribed herein will occur to those of ordinary skill in the artwithout departing from the spirit and the scope of the invention asclaimed. Accordingly, the invention is to be defined not by thepreceding illustrative description but instead by the spirit and scopeof the following claims.

1. A method for controlling pulsed power, comprising: measuring a firstpulse of delivered power from a power amplifier to obtain data;generating a first signal to adjust a second pulse of delivered power,the first signal correlated to the data to minimize a power differencebetween a power set point and a substantially stable portion of thesecond pulse; and generating a second signal to adjust the second pulseof delivered power, the second signal correlated to the data to minimizean amplitude difference between a peak of the second pulse and thesubstantially stable portion of the second pulse.
 2. The method of claim1 further comprising providing the second signal as an input to avoltage source, the voltage source providing a voltage to a voltage topower converter.
 3. The method of claim 2 further comprising correlatingthe second signal to a time delay measured between the voltage sourcereceiving a set point and the voltage to power converter outputtingpower.
 4. The method of claim 1 further comprising calculating a pulseshape error between the peak of the first pulse and the substantiallystable portion of the first pulse.
 5. The method of claim 4 furthercomprising correlating the second signal to the pulse shape error. 6.The method of claim 1 further comprising calculating a power offsetbetween the power set point and the substantially stable portion of thefirst pulse.
 7. The method of claim 6 further comprising correlating thefirst signal to the power offset.
 8. The method of claim 1 furthercomprising providing the first signal as an input to a voltage source,the voltage source providing a voltage to a voltage to power converter.9. The method of claim 8 further comprising correlating the first signalto a duty cycle input of the voltage source.
 10. A method of powerdelivery, comprising: delivering power from a power delivery system in acontinuous-wave mode to a load; generating a signal in a feedback loopto control the delivered power, the signal correlated to a power controlalgorithm; and adjusting a single variable in the power controlalgorithm to transition the delivered power from the continuous-wavemode to a pulsed mode.
 11. The method of claim 10 further comprisingactivating a switch in the feedback loop based on an input correspondingto the single variable, the switch in electrical communication with apower amplifier.
 12. The method of claim 10 further comprising filteringthe signal in the feedback loop to provide a substantially stable powermeasurement.
 13. The method of claim 10 further comprising providing thesignal as an input to a voltage source, the voltage source providing avoltage to a voltage to power converter.
 14. The method of claim 13wherein the signal is a duty cycle input of the voltage source.
 15. Themethod of claim 10 further comprising calculating a power offset betweena power set point and the delivered power.
 16. The method of claim 10further comprising measuring the delivered power to obtain data.
 17. Themethod of claim 16 further comprising generating a second signal toadjust a shape of delivered pulsed power, the second signal correlatedto the data to minimize an amplitude difference between a peak of apulse and a substantially stable portion of the pulse.
 18. The method ofclaim 17 further comprising correlating the second signal to a timedelay measured between a voltage source receiving a set point and avoltage to power converter outputting power.
 19. The method of claim 16further comprising correlating the signal to the data to minimize apower difference between a power set point and a substantially stableportion of a pulse.
 20. A method of power delivery, comprising:delivering power from a power delivery system in a continuous-wave modeto a load; measuring power delivered to the load; generating a signalindicative of the power delivered using a feedback loop to controlamplitude of the power delivered, the signal corresponding to a powercontrol algorithm; adjusting a single variable in the power controlalgorithm to deliver pulsed power to the load via the same feedbackloop.
 21. The method of claim 20 further comprising activating a switchin the feedback loop based on an input corresponding to the singlevariable, the switch in electrical communication with a power amplifier.22. The method of claim 20 further comprising filtering the signal inthe feedback loop to provide a substantially stable power measurement.23. The method of claim 20 further comprising providing the signal as aninput to a voltage source, the voltage source providing a voltage to avoltage to power converter.
 24. The method of claim 23 furthercomprising correlating the signal to a duty cycle input of the voltagesource.
 25. The method of claim 20 further comprising calculating apower offset between a power set point and the delivered power.
 26. Themethod of claim 20 further comprising measuring the delivered power toobtain data.
 27. The method of claim 26 further comprising generating asecond signal to adjust a shape of delivered pulsed power, the secondsignal correlated to the data to minimize an amplitude differencebetween a peak of a pulse and a substantially stable portion of thepulse.
 28. The method of claim 27 further comprising correlating thesecond signal to a time delay measured between a voltage sourcereceiving a set point and a voltage to power converter outputting power.29. The method of claim 26 further comprising correlating the signal tothe data to minimize a power difference between a power set point and asubstantially stable portion of a pulse.
 30. A system for deliveringpulsed or continuous-wave RF power to a load, comprising: a voltage topower converter coupled to an output of a voltage source, the voltage topower converter adapted to generate the pulsed RF power or thecontinuous-wave RF power; a RF power amplifier coupled to an output ofthe voltage to power converter, the RF power amplifier adapted todeliver RF power to the load; a pulse shape control loop coupled to anoutput of the RF power amplifier and a first input of the voltagesource, the pulse shape control loop adapted to minimize an amplitudedifference between a peak of the pulsed power and a substantially stableportion of the pulsed power, the pulse shape control loop adapted tooperate when the pulsed RF power is in a first mode; and a power setpoint control loop coupled to the output of the RF power amplifier and asecond input of the voltage source, the power set point control loopadapted to minimize a power difference between a RF power set point andthe RF power delivered to the load.
 31. The system of claim 30 whereinthe power set point control loop is coupled to an output of the voltagesource.
 32. The system of claim 31 wherein the power set point controlloop comprises a voltage offset circuit, the voltage offset circuitconfigured to measure a voltage offset between a voltage output from thevoltage source and a voltage setpoint from the power set point controlloop.
 33. The system of claim 30 wherein the power set point controlloop comprises a switch in electrical communication with the output ofthe RF power amplifier.
 34. The system of claim 33 wherein the switchhas a switching frequency correlated to a pulsing frequency of thepulsed RF power.
 35. The system of claim 30 further comprising amatching network coupled to an output of the voltage to power converterand an input of the load.
 36. The system of claim 30 wherein the powerset point control loop comprises an output conditioning module coupledto the second input of the voltage source and the pulse set pointcontrol loop, the output conditioning module providing a duty cycleinput to the voltage source.
 37. The system of claim 30 wherein thevoltage source is a buck regulator.
 38. The system of claim 30 whereinthe power set point control loop comprises a digital-to-analogconverter.
 39. A system for delivering pulsed or continuous-wave RFpower to a load, comprising: a voltage to power converter coupled to anoutput of a voltage source, the voltage to power converter adapted toproduce the pulsed RF power or the continuous-wave RF power; a RF poweramplifier coupled to an output of the voltage to power converter, the RFpower amplifier adapted to deliver RF power to the load; a first controlcircuit coupled to an output of the RF power amplifier and a current setpoint output; and a second control circuit coupled to an input of thevoltage source and an output of the voltage source, the second controlcircuit in electrical communication with the current set point output,wherein the first and second control circuits, in combination, areadapted to minimize a power difference between a RF power set point andthe RF power delivered to the load.
 40. The system of claim 39 furthercomprising a third control circuit coupled to the output of the voltagesource and a voltage set point output of the second control circuit. 41.The system of claim 39 wherein the first control circuit furthercomprises a switch in electrical communication with the output of the RFpower amplifier.
 42. The system of claim 39 further comprising at leastone filter in electrical communication with the switch and the output ofthe RF power amplifier.
 43. The system of claim 42 wherein the at leastone filter is adapted to provide a substantially stable powermeasurement.
 44. The system of claim 39 further comprising at least onefeed-forward input coupled to the second control circuit.
 45. The systemof claim 44 wherein the at least one feed-forward input comprises avoltage set point input.
 46. The system of claim 44 wherein the at leastone feed-forward input comprises a current set point input.
 47. Thesystem of claim 39 wherein the second circuit comprises a conditioningmodule, the conditioning module providing a duty cycle input to thevoltage source.
 48. The system of claim 39 further comprising a pulseshape control loop coupled to an output of the RF power amplifier and asecond input of the voltage source, the pulse shape control loop adaptedto minimize an amplitude difference between a peak of the pulsed powerand a substantially stable portion of the pulsed power, the pulse shapecontrol loop adapted to operate when the pulsed RF power is in a firstmode.